A series or parallel combination of individual cells, known as a battery, is used to provide a portable means for powering various stored energy appliances. A stored energy appliance is preferred over an alternating current supplied appliance when the location of the appliance changes frequently during operation, when handling of the appliance is hampered by a power cord, or when a source of alternating current is not available. A prime example of a stored energy appliance being preferred over an alternating current appliance is in the use of handheld power tools. Cordless handheld power tools are usually employed to repeatedly perform similar tasks over various locations, with the tasks being easier to perform without the presence of a power cord. Such cordless handheld power tools include handheld power drills, wire wrapping tools, and in-line and pistol grip power screwdrivers.
Many cordless power tools include the capacity therewithin for accommodating a battery assembly, the battery assembly comprising the series or parallel combination of cells contained within a battery housing. The battery assembly can be synonymously referred to as a battery pack or a power pack. Electrical contact is provided between terminals of the battery housing and corresponding powering contacts of the cordless power tool. The battery assembly is designed to be an entity separate from the cordless power tool so as to facilitate ease in both the removal and replacement of cells. Hence, when the cells in a battery assembly become discharged resulting from use of the power tool, or when the cells have lost their ability to retain a sufficient charge due to age, the entire discharged battery assembly can be removed and a new battery assembly containing either recharged cells or new cells can be inserted.
For the purpose of environmental protection, some retailers of appliances using battery assemblies are accepting aged or defective battery assemblies used in appliances which they retail, for either recycling or disposal. The consumer typically returns his/her old battery assembly when he/she purchases a new battery assembly. Employees of the retailer responsible for the exchange dispose the old battery assembly into a storage container. At a later time, the cells from within the battery assemblies in the storage container are removed for proper disposal or recycling.
Although each of the battery assemblies within the storage container may be either incapable of sufficiently powering the tool or altogether defective, generally, each is still sufficiently energized to generate a flow of electrical current if a conductive path is provided between the positive and negative terminals. Specifically, a significantly-high current flow can result when a cell with low internal impedance is externally shorted. The heat produced by such a high current can cause severe burns if contact is made with a person's skin. Further hazards resulting from the heat include the risk of explosion of the cells and the potential of fire. Therefore, care must be taken to prevent shorting of the terminals of the removed battery assemblies within the storage container.
A second common scenario in which a collection of battery assemblies is stored in a container results from the power demands of cordless power tools relative to the power storage capabilities of the cells. In order to complete a large-scale tooling job with a cordless power tool, many successive replacements of a discharged battery assembly with a charged battery assembly may be necessary. For example, a cordless power drill equipped with nickel-cadmium cells will run low on energy after a matter of minutes of application. The same applies for garden tools such as lawn mowers and hedge shears. An alternative to a procedure of repeatedly charging the cells in the discharged battery assembly (using a one-hour fast charger, for example) followed by performing a subset of the tooling tasks is to have a plurality of charged battery assemblies present to allow the completion of tooling tasks with minimal offtime. The depleted battery assemblies would then be discarded into a storage container to provide collection for recharging of the cells thereafter. An additional concern with regard to short circuiting the terminals in this scenario is the possibility of causing permanent damage to the cells by the act of forcible discharge. This is especially true for cells containing a light metal anode, such as lithium.
U.S. Pat. No. 4,265,984 to Kaye discloses a two-piece battery housing comprising two terminals located at the same end of the housing. One of the housing terminals, electrically connected to a terminal of the battery, is recessed within the housing, while the other of the housing terminals, electrically connected to the other terminal of the battery, protrudes from the battery housing concentric with and spaced from the first terminal. Although this configuration of the terminals prevents inadvertent short circuiting of the batteries if stored in bulk, short circuiting can easily occur if a stray conductive object, such as a screw or a nut, contacts the assembly so as to provide a conductive path between the two terminals.